U.S. patent application number 14/745299 was filed with the patent office on 2015-12-24 for system for converting electromagnetic radiation to electrical energy using metamaterials.
The applicant listed for this patent is Patrick K. Brady, Dale K. Kotter, Wounjhang Park. Invention is credited to Patrick K. Brady, Dale K. Kotter, Wounjhang Park.
Application Number | 20150372621 14/745299 |
Document ID | / |
Family ID | 54870558 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150372621 |
Kind Code |
A1 |
Brady; Patrick K. ; et
al. |
December 24, 2015 |
System for Converting Electromagnetic Radiation to Electrical
Energy Using Metamaterials
Abstract
Spectral tuning of heat source to emit radiation at a desired
frequency or frequency band is accomplished using metamaterials.
The metamaterials include a structured geometry having holes with
dimensions and spacing chosen such that the resulting surface will
emit radiation in the desired spectrum. A collector can be made of
a similar metamaterial or antenna array to detect the emitted
radiation and transfer it to a converter device that converts the
detected radiation to electricity. Embodiments also provide
efficient coupling to the converter device for energy harvesting.
Cooling of the converter devices can be accomplished using a
cooling sink or deep space.
Inventors: |
Brady; Patrick K.; (Glen
Ellyn, IL) ; Kotter; Dale K.; (Shelley, ID) ;
Park; Wounjhang; (Superior, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brady; Patrick K.
Kotter; Dale K.
Park; Wounjhang |
Glen Ellyn
Shelley
Superior |
IL
ID
CO |
US
US
US |
|
|
Family ID: |
54870558 |
Appl. No.: |
14/745299 |
Filed: |
June 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62015121 |
Jun 20, 2014 |
|
|
|
Current U.S.
Class: |
310/306 |
Current CPC
Class: |
H01L 31/00 20130101;
H02N 11/002 20130101; G02B 1/002 20130101; H01L 31/0264 20130101;
H01L 31/04 20130101; H01Q 1/248 20130101; Y02E 10/52 20130101 |
International
Class: |
H02N 11/00 20060101
H02N011/00 |
Claims
1. A system to convert heat into electricity, comprising: a
metamaterial having a surface that is tuned to generate an enhanced
electric field at a desired frequency; and a rectenna placed over
the enhanced electric field, at a distance to interact with the
generated electric field, and to produce electricity from the
generated electric field.
2. The system of claim 1, wherein the surface of the metamaterial
comprises a plurality of holes with dimensions and spacing to cause
the surface to generate the enhanced electric field at the desired
frequency, and wherein a rectenna is placed over each hole.
3. The system recited in claim 2, wherein each rectenna is placed
in the near field over the holes at less than 0.5 wavelengths of
the desired frequency.
4. The system recited in claim 1, wherein the rectenna comprises:
an antenna tuned to the desired frequency to interact with the
generated electric field to generate an electric current in an
antenna element; and a transfer structure to convert the electric
current into direct current.
5. The system recited in claim 1, further comprising at least one
lead to carry the direct current to power another device or to an
electricity storage device.
6. The system recited in claim 1, further comprising a cold source
to act as a cold sink to cool the rectenna.
7. The system recited in claim 1, further comprising a thermally
insulating and radiation transparent material placed between the
surface of the metamaterial and the rectenna.
8. The system recited in claim 7, wherein the rectenna comprises an
antenna element, further comprising a thermally conductive material
to couple the antenna element to a cold source.
9. The system recited in claim 8, further comprising a thermally
insulating material on either side of the thermally conductive
material to prevent heat loss from a heat source.
10. The system recited in claim 1, wherein the hole dimensions and
spacing form a periodic pattern on the surface of the
metamaterial.
11. The system of claim 1, wherein the surface of the metamaterial
comprises a plurality of posts with dimensions and spacing to cause
the surface to generate the enhanced electric field at the desired
frequency.
12. The system recited in claim 11, wherein deep space is used as a
cold sink for the rectenna.
13. The system recited in claim 11, wherein the rectenna is placed
in the near-field over each post at less than 0.5 wavelengths of
the desired frequency.
14. The system recited in claim 11, wherein the post is has a
height greater than one quarter of the wavelength of the desired
frequency.
15. The system recited in claim 11, further comprising a thermally
insulating and radiation transparent material surrounding each
post.
16. The system recited in claim 11, further comprising an
environmental overcoat to reflect away out-of-band energy.
17. The system recited in claim 11, wherein the desired frequency
has a wavelength in the bands of one of 3 .mu.m to 5 .mu.m and 8
.mu.m to 12 .mu.m.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/015,121, filed Jun. 20, 2014, which is hereby
incorporated by reference herein in its entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention relate generally to
structures and methods for harvesting energy from electromagnetic
radiation and, more specifically, to nanostructures, metamaterials
and related methods and systems for harvesting energy from, for
example, infrared, near infrared and visible spectrums and
capturing millimeter waves and Terahertz energy.
[0004] 2. Background of the Invention
[0005] There is a great need for inexpensive renewable energy in
the world right now. Ironically, there is an abundance of energy
available in the form of sunlight and heat but using it to support
the needs of society requires it to be converted into electrical
form. Most electrical energy used today comes from a conversion
process involving heat. Nuclear, coal, diesel, and natural gas
powered electrical generation plants all convert stored forms of
energy into heat for conversion into electricity. Processes in
these plants are inefficient and often produce more heat as waste
than is converted into electricity.
[0006] Harvesting sources of heat into usable electrical power is
especially desirable at low cost. The cost of turbine based
solutions is well established at this point. As a result, new
technological solutions for converting heat to electrical power
enter a relatively mature environment. Because of the need and the
fixed pricing environment, new technologies are beginning to
address this area. These new technologies include thermo
photovoltaic (TPV), thermoelectric (TE) and organic rankine cycle
(ORC) systems.
[0007] TPV technology has encountered difficulties with heat
conversion applications since photovoltaic (PV) converts short wave
radiation, not the long waves found in the infrared (IR) and near
IR spectra associated with heat. New micron gap methods for
bringing such long wave energy to the PV cell still require
conversion technology better suited to this influx of long wave
radiation. The PV cell band gap favors only energetic photons since
lower energy photons do not have the energy to surmount the gap and
end up absorbed, thereby causing heat in the PV cell.
[0008] Thermoelectric has only been able to convert heat to
electrical power at low efficiency. To date, TE applications for
converting heat to electricity has been unable to provide
substantial efficiencies in energy conversion. Despite these
hurdles, TE has been used in automotive waste heat recovery, which
further demonstrates the need for alternative heat-to-electric
conversion technologies.
[0009] Organic Rankine Cycle technology harvests waste heat by
chaining turbines together with heat exchangers each with a lower
boiling point liquid in its system. Unfortunately, ORC systems are
bulky and have large numbers of moving parts. They are also limited
to the properties of the liquids and ultimately the limit of time,
space and marginal results of additional systems in a working
space.
BRIEF SUMMARY OF THE INVENTION
[0010] The technology of surfaces of paired nanoantenna and diode
arrays present tremendous advantages for energy harvesting
applications. In the area of waste heat recovery these systems are
ideal since they have no moving parts, are inexpensive to
manufacture and can be tuned to the frequency spectra of the target
source. The ability to tune the collecting elements of the system
to the spectral properties of the source make these technologies
ideal not only for waste heat applications but for heat harvesting
in general and, ultimately, solar energy harvesting as well.
[0011] Embodiments described herein involve a method for tuning to
the spectral properties of a heat source using metamaterial
designs. The combination of collector and source tuning make this a
powerful method for harvesting energy from a variety of sources.
Beyond tuning of source and collecting elements, embodiments
described herein use methods that enable thermal energy to be
efficiently coupled into nanostructures for energy harvesting.
[0012] In embodiments, a metamaterial device acts as converter
between propagating and localized electromagnetic fields, providing
an effective route to couple photons into the antenna-based energy
harvesters. This structure can exceed the black body radiation
limit. The collector array components of these systems are called
Nanoantenna Electromagnetic Collectors (NEC).
[0013] Various nanostructure-based metamaterial surface treatments
have been developed to enhance energy capture from thermal heat
sources. Metamaterial layers tune the thermal emissions of a hot
body to radiate energy in the channels optimized for high
efficiency energy conversion. Methods are demonstrated for
affordable, large-scale fabrication of the device.
[0014] Embodiments of the present invention also include systems
and methods to harvest electromagnetic radiation from far-field
plane waves, to harvest EM radiation from near-field evanescent
and/or plasmonic waves, and to harvest electromagnetic radiation
using a combination of far- and near-field effects. Systems and
apparatus for energy capture and concentration include resonant
antenna structures and metamaterial films. Systems and apparatus
for energy conversion include various types of rectification
processes integrated with the antenna device, which is also
referred to herein as a rectenna. Energy conversion apparatus and
methods include, but are not limited to: metal-insulator-metal
(MIM), metal-insulator-insulator-metal (MIIM), and Traveling Wave
Diode (TWD) diode devices.
[0015] In an embodiment, the present invention is an energy
harvesting system that includes resonant elements tuned to
frequencies in the range of available radiant energy. Typically,
such frequencies are in the frequency range from approximately 10
THz, in the infrared, to over 1000 THz (visible light). In an
embodiment, these resonant elements are composed of electrically
conductive material, and coupled with a transfer element. The
transfer element converts stimulated electrical energy in the
resonant element to direct current, to form resonant and transfer
element pairs. In an embodiment, the resonant element and transfer
element pairs are arranged into arrays that are embedded in a
substrate and interconnected to form a power source, for example,
for an electrical circuit or other apparatus or device requiring
sourced electrical energy to operate. Additional details for
resonant and transfer elements of embodiments are described in U.S.
patent application Ser. No. 13/708,481, filed Dec. 7, 2012,
entitled, "System and Method for Converting Electromagnetic
Radiation to Electrical Energy," (U.S. Pat. App. Pub. No. US
2013/0146117) (the "'481 application"), U.S. patent application
Ser. No. 14/108,138, filed Dec. 16, 2013, entitled, "System and
Method for Identifying Materials Using a THz Spectral Fingerprint
in a Media with High Water Content" (U.S. Pat. Pub. No. U.S.
2014/0172374) (the "'138 application"), and U.S. patent application
Ser. No. 14/187,175, filed Feb. 21, 2014, entitled, "Structures,
System and Method for Converting Electromagnetic Radiation to
Electrical Energy" (copy attached to U.S. Provisional App.
62/015,121 as Appendix A, which is hereby incorporated by reference
herein in its entirety) (the "'175 application"), each of which is
hereby incorporated by reference herein in its entirety.
[0016] In addition to the resonant and transfer elements described
above, in an embodiment, the surface of the material is modified to
be a metamaterial. The metamaterial enables the surface to radiate
energy that matches the spectrum of the NEC components that will
harvest it. In an embodiment, the metamaterial comprises a grid of
holes of specific depth, area, and spacing. These holes produce an
artificial surface resonance at a specific frequency. This
operation is similar to surface plasmons on metal surfaces. The
electromagnetic field is concentrated over the holes where NEC
devices may be placed. Furthermore, the energy available for
harvesting is most concentrated in the near field, which is defined
as the region within the light wavelength from the surface. In one
embodiment, a NEC is placed 3 .mu.m above each hole and the surface
and NEC are tuned to 1 THz. In another embodiment, a NEC is placed
in the near-field over each hole at less than 0.5 wavelengths of
the specific frequency that causes surface resonance. In
embodiments, a NEC is placed over some, but not all of the holes.
In an embodiment, the specific dimensions of holes and hole
placement are determined by computer simulations based on the
Maxwell's equations describing the interaction between light and
material. For example, in an embodiment, hole spacing is 50 .mu.m,
hole diameter is 10 .mu.m and hole depth is 40 .mu.m. The
simulation software used was COMSOL available from COMSOL, Inc. and
Lumerical, available from Lumerical Solutions, Inc.
[0017] In an embodiment, components, elements and substrate of the
device are composed of metals and materials that allow them to be
manufactured in low cost methods such as roll-to-roll.
[0018] In an embodiment, the present invention is a system to
convert heat into electricity that includes a metamaterial having a
surface that is tuned to generate an enhanced electric field at a
desired frequency and a rectenna placed over the enhanced electric
field, at a distance to interact with the generated electric field,
and to produce electricity from the generated electric field. In an
embodiment, the surface of the metamaterial comprises a plurality
of holes with dimensions and spacing to cause the surface to
generate the enhanced electric field at the desired frequency, and
wherein a rectenna is placed over each hole. In another embodiment,
the surface of the metamaterial comprises a plurality of posts with
dimensions and spacing to cause the surface to generate the
enhanced electric field at the desired frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1A is a graph of electric field at the surface of a
metal supporting surface plasmon resonance
[0020] FIG. 1B is a graph of electric field strength as a function
of distance above and below the surface in the metal.
[0021] FIG. 2 is a graph illustrating the local density of states
versus frequency at different heights above a semi-infinite sample
of aluminum.
[0022] FIG. 3 is a graph illustrating the emitted energy, at
various distances from the surface of a metal, per unit volume per
unit frequency across a wide spectrum of frequencies.
[0023] FIGS. 4A and 4B illustrate the inter-relationship of
elements of one metamaterial structure that generates plasmonic
resonance on the surface of a metal.
[0024] FIGS. 5A and 5B illustrate a cross sectional view of the
metamaterial structure elements.
[0025] FIGS. 6A and 6B illustrate a 3-dimensional view of electric
field strength simulation results for a rectenna placed near one of
the holes in the surface of a metamaterial.
[0026] FIG. 7 is a cross sectional view of a metamaterial structure
with a rectenna placed at the structure aperture.
[0027] FIG. 8 illustrates a cross sectional view of a system that
can harvest the earth's heat.
[0028] FIG. 9 illustrates a 3-dimensional view of the system of
FIG. 8.
[0029] FIG. 10 illustrates an embodiment in which THz sources are
matched up with THz sensors to provide electrical output carried
via an electrical bus to provide power to an electrical device.
DETAILED DESCRIPTION
[0030] The following description is presented to enable one of
ordinary skill in the art to make and use the invention and is
provided in the context of a patent application and its
requirements. Various modifications to the described embodiments
will be readily apparent to those skilled in the art and the
generic principles herein may be applied to other embodiments.
Thus, the present invention is not intended to be limited to the
embodiments shown but is to be accorded the widest scope consistent
with the principles and features described herein.
[0031] FIG. 1A is a graph of electric field at the surface of a
metal supporting surface plasmon resonance. FIG. 1B is a graph of
electric field strength as a function of distance above and below
the surface in the metal where .delta..sub.d is the distance above
the surface, and .delta..sub.m is the distance below the surface.
FIG. 2 is a graph showing the local density of states versus
frequency at different heights above a semi-infinite sample of
aluminum. The local density of states represents the number of
available photon states and the larger local density of states
naturally enables higher optical power density. FIG. 2 shows the
local density of states is strongly enhanced at the surface plasmon
frequency and this means strongly enhanced optical power density
may be achieved at that frequency. The surface plasmon frequency of
metal is not engineerable. It is thus necessary to adopt the
metamaterial concept which allows us to design an artificially
structured surface whose surface plasmon frequency can be tuned.
FIG. 3 is a graph of the emitted energy, at various distances from
the surface of a metamaterial designed to exhibit surface plasmon
modes at 1 THz, per unit volume per unit frequency across a wide
spectrum of frequencies. It shows strongly enhanced optical energy
density at the surface plasmon frequency.
[0032] FIGS. 1A, 1B, 2, and 3 demonstrate that a metamaterial can
be engineered to generate an electric field having an enhanced
field strength at a resonant frequency that is tunable. As
described below, in embodiments, a metamaterial is designed to
exhibit resonance, and therefore an enhanced electric field, in the
presence of frequencies associated with heat. A rectenna is placed
in the electric field to convert the energy in the electric filed
to electricity. In an embodiment, a rectenna is a device having
antenna elements responsive to the electric field and a transfer to
device such as a MIM or MIIM diode that converts the radiated
energy from the antenna elements to electricity.
[0033] FIGS. 4A and 4B are schematic diagrams of an exemplary
metamaterial structure at the surface of a hot object 408. Holes
401 are fabricated in surface 405 using lithographic and etching
methods known to those skilled in the art. In an embodiment, the
size (or area) of holes 401, represented by dimensions 402 (length)
and 403 (width), the spacing 406 between holes 401, and the depth
407 of holes 401 are determined by simulation of electromagnetic
waves incident on hot surface 405 and elements of structure 408 so
that the metamaterial surface supports a strong surface resonance
at or near a desired frequency. In embodiments, the desired
frequency is 1 THz. An exemplary such surface resonance near 1 THz
is illustrated in FIGS. 2 and 3. In an embodiment, for example, the
simulation numerically solves Maxwell's equations with a given
geometry. FIG. 4B shows an exemplary geometry used for
3-dimensional simulations in a particular embodiment. In the
embodiment, the hole has surface dimensions a and b, to represent
width and length respectively. Where dimensions a and b are equal,
i.e., the hole is square, resonant frequency can be approximated
by:
.omega. pl = .pi. c 0 a H .mu. H ##EQU00001##
where .omega..sub.pl is the effective plasmon resonant frequency,
c.sub.0 is the speed of light, a is the size of the holes,
.epsilon..sub.h is the electric permittivity and .mu..sub.h is the
magnetic permeability of the material.
[0034] Electromagnetic waves such as light exhibit polarization.
Various states of polarization can occur from
environmental/material boundary conditions that induce scatter and
absorption. Metamaterials can be designed to respond and extract
energy from various modes of polarization. For example, if
dimensions a and b are not equal, i.e., the hole is rectangular,
the metamaterial becomes anisotropic and exhibits difference
responses to different polarizations. Similarly in an embodiment,
spacing d in the x direction may be different than spacing d in the
y direction. Where spacing d is different in the x and y
directions, the metamaterial becomes anisotropic and exhibits
difference responses to different polarizations.
[0035] FIGS. 5A and 5B illustrate an exemplary geometry used for a
2-dimensional simulation to determine hole dimensions and hole
spacing to achieve a desired resonant frequency according to an
embodiment. In an embodiment, hole spacing and dimension form a
periodic structure of holes 401 in metamaterial 408. As such, the
exemplary simulation can be simplified by using a computational
cell containing only one unit cell with a periodic boundary
condition. For the direction perpendicular to the metamaterial
surface, an absorbing boundary condition was used to simulate the
infinite extent of the medium. In FIG. 5A, the dimensions are
designated by 402, 403, and 407 for length, width, and depth
respectively, with a hole spacing 406. In FIG. 5B, the dimensions
are designated as a (area of the hole), d (depth of the hole), and
p (hole spacing).
[0036] In a typical simulation, a plane wave with a fixed
wavelength is launched onto the metamaterial surface and the
subsequent reflected power is calculated. This simulation is
repeated over a range of wavelengths to obtain a reflectance
spectrum. The reflectance spectrum should exhibit a dip at the
wavelength of surface plasmon resonance. The geometry (dimensions
and spacing of the holes) of metamaterial surface is then tuned to
shift the resonance dip in the reflectance spectrum into the
desired wavelength. Full optimization should also include
minimizing the line width and maximizing the depth of the
reflection dip because these conditions correspond to the strongest
resonance.
[0037] In the simulation using the plane wave as described above,
the incident wave must couple to the surface wave in order to
produce a dip in the reflectance spectrum. This is achieved by the
periodicity of the holes which acts as a grating and imparts a
momentum necessary for coupling to the surface wave. Specifically,
the grating coupling condition is given as:
.beta. = 2 .pi. .lamda. sin .theta. + 2 .pi. .rho. ##EQU00002##
where .lamda., .theta., and .rho. are the wavelength, incident
angle and grating period, respectively. When the propagation
constant .beta. matches that of the surface wave, the incident wave
will couple to the surface wave, resulting in a dip in the
reflectance spectrum.
[0038] While coupling occurs whenever this condition is met, the
coupling efficiency may vary. Thus some structures may not show
prominent reflectance dips even though surface waves do exist. In
order to avoid missing surface waves due to poor coupling
efficiency, dipole sources are used in the simulation. Dipole
sources are basically harmonically oscillating point dipoles. An
oscillating point dipole produces an electromagnetic wave emanating
isotropically. By placing many point dipole sources on the
metamaterial surface coupling into the surface wave is ensured. In
this case, the existence of surface wave would be detected by
monitoring the electric and magnetic field patterns near the
surface. A strong enhancement of field intensity near the surface
signifies the presence of surface wave.
[0039] Resonances form on the surface of material 408 at the tuned
frequency of interest. In an embodiment, this frequency is 1 THz.
Materials 408 can be a variety of materials, including, for
example, copper, or any other highly conductive material. Other
materials may be used if design dimensions are recalculated by
simulation as described above. In an embodiment, metamaterial 408
is copper with a thickness of 100 .mu.m. Dimensions for the
embodiment are 10 .mu.m for hole length 402, 10 .mu.m for hole
width 403, 50 .mu.m for hole spacing 406 and 40 .mu.m for hole
depth 407.
[0040] FIGS. 6A and 6B illustrate schematically a rectenna 601
placed over a hole 401 with field intensity mapping. Rectenna 601
comprises antenna elements 601a and 601b, and a diode 602. Placing
rectenna over a hole 401 in the surface of a metamaterial as shown
in FIGS. 6A and 6B is to deliver a concentrated electric field to
antenna elements 601 and thereby to diode 602, where harvesting of
radiant energy to electricity occurs. Once radiant heat energy is
harvested it is carried to a bus structure via leads 603 and 604,
and can be used to power electronic devices or to electricity
storage facilities. Additional details for rectenna 601 are
described in the '481 application, the '138 application and the
'175 application.
[0041] FIG. 7 illustrates a cross sectional view of a metamaterial
408 with a rectenna 601 that comprises antenna elements 601a and
601b and a diode 602. In the embodiment shown in FIG. 7, hole 401
is filled with a highly insulating material 708. Exemplary highly
insulating materials 708 include SUB, Aerogel, air, and vacuum.
Material 708 must be insulating but transparent to radiation.
Rectenna 601 is set at a distance 703 from the surface of the
metamaterial 408. This distance is important since the power of the
electric field decreases exponentially with distance from the
surface. In one embodiment the distance is at or approximately 3
.mu.m which offers a good balance of thermal insulation and
proximity for field strength. In another embodiment, rectenna 601
is placed in the near-field over hole 401 at less than 0.5
wavelengths of the specific frequency that causes surface
resonance. In an embodiment with a plurality of holes 401, a
rectenna 601 is placed over each hole 401. In an embodiment with a
plurality of holes 401, a rectenna is placed over some, but not
all, holes 401.
[0042] Materials 706 and 707, on top of rectenna 601, conduct heat
and couple the rectenna 601 to a cold source 710. Materials 704 and
705, which surround rectenna 601, are insulating to prevent lost
heat from the source 701 and serve to guide heat via radiation to
rectenna 601.
[0043] FIG. 8 illustrated an embodiment of the present invention
that is configured to harvest heat from the Earth in the context of
the low temperature of deep space. In such embodiment, deep space
acts as the cooling source for a rectenna 1101. As shown in FIG. 8,
rectenna 1101 is placed in the near field of post metamaterial
structure 1104. Post structure 1104 concentrates the electric
field, generated by a surface from heat delivered by a terrestrial
source (e.g., Earth), and delivers this electric field at a
frequency set by the design of the surface metamaterial structures
using a simulation as described above. To maximize the Carnot
system advantages of this system it is desirable to tune rectenna
1101 to a frequency in a clear band of the Earth's atmosphere. Two
such bands are well known: 3 .mu.m to 5 .mu.m and 8 .mu.m to 12
.mu.m. Rectennas tuned in this band will radiate freely with the
cold source of deep space and create a system whose Carnot zone is
nearly 100% (C=1-Tc/Th; where Tc=3K and Th=300K).
[0044] In an embodiment using deep space as a cold source, as shown
in FIG. 8, the metamaterial is in the form of a plurality of posts
1104, rather than holes 401, one of which is shown in FIG. 8. In an
embodiment, a plurality of posts are placed periodically as
described above for holes 401. Post 1104 is surrounded by a heat
insulating and radiation transparent material 1103. An exemplary
such material 1103 is Aerogel. In another embodiment, material 1103
is replaced with a vacuum to optimize thermal insulation
properties. In an embodiment, rectenna 1101 is placed at or
approximately 2 .mu.m above post 1104. In another embodiment, a
rectenna 1101 is placed in the near-field over post 1104 at less
than 0.5 wavelengths of the specific frequency that causes surface
resonance. In an embodiment, a rectenna 1101 is placed over some
but not all posts 1104. In an embodiment, post 1104 is at least the
height of 1/4 wavelength of the tuned frequency of rectenna 1101.
Post design 1104 allows an element of rectenna 1101 to radiate into
space 1106 since it is more than a quarter wavelength away from the
surface of the metal. The combination of near proximity to post
1104 and greater than quarter wavelength to the surface metal 1105
allows rectenna 1101 to receive energy from the tuned metamaterial
1104 yet still radiate into deep space 1106.
[0045] It is advantageous for the tuned frequency of rectenna 1101
to equal the tuned frequency of the metamaterial 1104 so surface
plasmons will deliver energy most efficiently to the rectennas
1101. Also, rectennas 1101 need to be tuned within the clear band
regions of the atmosphere.
[0046] The system illustrated in FIG. 8 harvests energy as
electricity since rectenna 1101 is stimulated into oscillation by
terrestrial heat. A source of efficiency in embodiments results
from the reflection of energy coming from nearby terrestrial
sources that is in the bands outside the clear atmospheric windows.
The system needs to reflect away this "out of band" energy for
rectenna 1101 to stay cooled by deep space 1106.
[0047] This is part of the purpose of environmental overcoat 1102.
Environmental overcoat 1102 is heat insulating and radiation
transparent in the "in band" wavelengths of the atmosphere, i.e.,
in the clear band. Directionality is also an important factor in
design. Because the system is in contact with the sky, rectennas
1101 need to be pointed toward the sky and not obscured by
intervening objects.
[0048] FIG. 9 illustrates a plurality of such elements.
Metamaterial posts 1104 on surface 1105 create the plasmonic
structure that concentrates a plasmonic electric field at the tips
of the post structures. Rectennas 1101 are placed in the near field
of this structure and tuned for near field resonance at the
plasmonic frequency. The tuning of rectenna 1101 must also match a
portion of the transparent window in the atmosphere.
[0049] If an antenna is substituted for rectenna 1101 in the
embodiment illustrated in FIGS. 8 and 9, the system converts heat
energy to radiation at the tuned frequency of the antenna. Such a
system has significant advantages for use as an inexpensive source
of THz radiation. In particular, surfaces covered with THz tuned
antennas (matched to tuned metamaterial 1104) generate THz
radiation at very low cost. The entire THz range can be generated
by covering a surface 1105 with subregions of the surface tuned to
subregions of the THz spectrum (both antennas and
metamaterials).
[0050] FIG. 10 illustrates a system for generating THz radiation
according to an embodiment. THz sources layers 1202 are matched up
with THz sensors 1204. THz source layers 1202 and THz sensors 1204
can be as those described in the '481 application, the '138
application and the '175 application.
[0051] As illustrated in FIG. 10, a heat source 1201 generates
heat. A THz source layer 1202 comprises a THz metamaterial and an
antenna tuned to THz frequencies. In response to the heat generated
by heat source 1201, the metamaterial in THz source layer 1202
generates energy at the tuned THz frequencies. The antenna devices
in THz source layer 1202, which are also tuned to the THZ
frequencies, radiate THz radiation to THz detectors 1204. THz
detectors 1204 respond to the radiated THz radiation to provide
electrical output carried via electrical bus 1205 to provide power
to an electrical device, for example, a computer 1206, which can
include, among other things, for example, digital processing
capabilities, storage, and display. In an embodiment, THz sources
1202 are such as described above with respect to the antenna
variation described above with respect to FIGS. 8 and 9. This
system provides active illuminated THz detection at low cost at
standoff distances. Both the THz sources 1202 and detectors 1204
are tunable within the THz range so such a system is highly
flexible and deployable to a variety of applications.
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